344 P s t e I s i a 



may be caught showing that the calcium car- 

 bonate is in the form of Lirge rhombohedra of 

 calcite. If the imprisoned grains of quartz 

 coukl ])c removed, the calcite would show a 

 texture as coarsely crystalline as is frecjuently 

 seen in vein calcite. In other words, the calcium 

 carl:)onate, in undergoing a molecular transition 

 from the organic to the mineral stage, envelopes 

 the grains of quartz and other contents of the 

 concretionary mass in precisely the same form 

 it would assume in being deposited as vein cal- 

 cite in a coarsely crystalline mineral vein. Thus, 

 there is present in these interesting structures an 

 exhibition of the strength of the force of crys- 

 tallization. Although exercised upon a very 

 common rock constituent, the result is clearer 

 than is usually seen in rock formations of any 

 geologic age or type of rock. It is doubtless 

 force of crystallization which underlies the nota- 

 ble symmetry of these bodies. A large rhom- 

 bohedron of calcite, rounded off, would have a 

 form like most of the larger so-called concretions 

 of this coast. Crystallization has drawn the 

 calcite around these nuclei from among adjacent 



